NOTE: As their name suggests hints are not exactly Inversion cheats, and are usually just simple (but very useful) tips on how you can unlock secret level, features, find hidden areas and such. Hopefully these will make playing Inversion even more entertaining.

Achievements
Complete each achievement to get the allotted gamerscore.
Ah Gross! (5): Use the Gravlink to throw a corpse at your friend (Co-op mode)
All Up In Them Guts (25): Use a Shotgun to gib 25 Lutadore enemies (Any Difficulty)
Brotastic! (5): Revive a friend online (Co-op mode)
Burn it Down (25): Set 25 Lutadore enemies on fire with the Lavagun (Any Difficulty)
Chapter Eight (10): Complete the final checkpoint in Into the Depths on Normal or High Difficulty
Chapter Eleven (10): Complete the final checkpoint in Red Sky on Normal or High Difficulty
Chapter Five (10): Complete the final checkpoint in Street Fight on Normal or High Difficulty
Chapter Four (10): Complete the final checkpoint in Road Home on Normal or High Difficulty
Chapter Nine (10): Complete the final checkpoint in Enlightenment on Normal or High Difficulty
Chapter One (10): Complete the final checkpoint in Vanguard Down on Normal or High Difficulty
Chapter Seven (10): Complete the final checkpoint in Edge of the World on Normal or High Difficulty
Chapter Six (10): Complete the final checkpoint in Road to Hell on Normal or High Difficulty
Chapter Ten (10): Complete the final checkpoint in Reveal on Normal or High Difficulty
Chapter Thirteen (10): Complete the final checkpoint in Reversion on Normal or High DifficultyChapter Three (10): Complete the final checkpoint in Breakout on Normal or High Difficulty
Chapter Twelve (10): Complete the final checkpoint in Deja Vanguard on Normal or High Difficulty
Chapter Two (10): Complete the final checkpoint in Caged on Normal or High Difficulty
Dude Bro! (5): Complete a Campaign level with a Friend (Any Difficulty)
Easy Going (25): Finish the Campaign on Low Gravity Difficulty
Enforcer (25): Reach Gold Grav Major Rank
Feats Don't Fail Me Now (50): Complete All Multiplayer Basic Challenges
Fivesome (50): Use the Gravlink to kill 5 Lutadores with one object (Campaign)
Gold Star (10): Get 1st Place in a Deathmatch game (Matchmaking)
Grappler (25): Take the Gravlink from the Lutadores
Gravlink Gangsta (25): Use the Gravlink to throw 50 Lutadore Enemies (Campaign)
Gravlink Hustler (15): Use the Gravlink to throw 30 Lutadore Enemies (Campaign)
Gravlink Thug (10): Use the Gravlink to throw 15 Lutadore Enemies (Campaign)
Half Sack (5): Reach Silver Grav Sergeant Rank
High G Amateur (15): Perform 10 Finishing Moves using High Grav Powers (Campaign)
High G Champ (25): Perform 50 Finishing Moves using High Grav Powers (Campaign)
I'm About to Blow (25): Kill 100 Lutadore Enemies with explosives in the Campaign (Grenades, Rockets, Barrels)
I'm Designer (5): Change your multiplayer character's appearance
Kicking Weightless Ass (10): Escape from a Lurker's grasp 5 times during single player
Low G Amateur (15): Perform 10 Finishing Moves using Low Grav Powers (Campaign)
Low G Champ (25): Perform 50 Finishing Moves using Low Grav Powers (Campaign)
Man of Mayhem (50): Reach Diamond Grav Commander Rank
Master Blaster (50): Complete All Multiplayer Weapon Challenges
Meatheads (50): Finish the Campaign with a Friend (Any Difficulty)
Meet Your Master (15): Defeat The Prophet Kiltehr (Any Difficulty)
Normal Guy (50): Finish the Campaign on Normal Gravity Difficulty
Rock Hard (75): Finish the Campaign on High Gravity Difficulty
Soldier (15): Reach Bronze Grav Captain Rank
Spot me Bro! (5): Have a friend boost you over a ledge (Co-op mode)
Teamster (15): Be a part of a winning team in Team Deathmatch (Matchmaking)
That's Assault Brotha! (15): Be a part of a winning team in Assault Mode (Matchmaking)
The Collector (10): Defeat The Slave Driver (Any Difficulty)
The Great Destroyer (10): Defeat The Brute (Any Difficulty)
The Tin Man (10): Defeat The Butcher (Any Difficulty)
Threesome (25): Use the Gravlink to kill 3 Lutadores with one object (Campaign)
William Tell Routine (50): Shoot off 100 Lutadore Helmets (Any Difficulty)